1. Field of the Invention
The present invention relates to a device for orienting and angularly positioning the axis of rotation of a rotatable load.
Such a device is appropriate to an apparatus including a periodically turned load, and which has appropriate drive means and sensing means for detecting the amount of rotation, and which needs the axis of rotation of the load to be orientated relative to an origin position. Applications for such a device occur in the fields of measuring and controlling instruments, machine tools, robotics, helix agitators, and various other orienting mechanisms, for example the positioning equipment of optical or radio-astronomy telescopes. There are, of course, many other applications for such a device.
For the purposes of illustration, prior art devices of this type and the device of the present invention will be described with reference to their application to the orienting and angular positioning of the axis of rotation of a radio frequency dish antenna intended, for example, for the dynamic tracking of a non-stationary satellite.
2. Description of the Prior Art
A typical prior art orienting and positioning device for use with such a dish antenna is illustrated in FIG. 1. The device includes a fixed member 3 which is generally constituted by a tower on which a load support member 2 termed the "azimuth assembly" is mounted. The upper part of this azimuth assembly 2 rotates about the vertical axis, and on this support member a sighting assembly 5 is fixed. The sighting assembly comprises a horizontal axle which allows articulation of an antenna support assembly 1 which is called the "antenna".
The movable plate of the azimuth assembly 2 together with the sighting assembly 5 and the antenna 1 represent a rotatable load. Rotation of this load with respect to the tower 3 is normally provided by a motor drive and is sensed by measuring means such as an angular coder or potentiometer. The azimuth assembly 2 is mounted on the tower 3 in a horizontal plane.
Such a device as described with respect to FIG. 1 therefore requires separate motor drives for driving the azimuth assembly 2 in rotation about a vertical axis and the sighting assembly 5 about a horizontal axis.
Another type of prior art orienting and positioning device is illustrated with respect to FIGS. 2 to 5. In this arrangement an additional intermediate member 4 is positioned between the tower 3 and the azimuth assembly 2. This intermediate member is termed a wedge in the following discussion. The wedge defines two mounting planes and at least one of these planes is inclined with reference to the horizontal plane. The wedge is mounted so that it can be rotated relative to each of the members to which it is adjacent.
An initial or position of origin is illustrated in FIG. 2 in which the wedge 4 is disposed so that the rotation axis of the azimuth assembly is aligned with a vertical reference axis of the tower. In the position illustrated in FIG. 4, the wedge is disposed so that the rotation axis of the azimuth assembly 2 is shifted by an angular amount B relative to the reference axis of the tower 3.
FIGS. 3 and 5 illustrate the effect of the normal use of such a wedge. Rotation of the wedge through 180.degree. relative to its origin position as illustrated in FIG. 2 results in the rotation axis of the rotatable load 1, 2 and 5 being displaced by an angular value 2A relative to the reference axis of the tower, where A is the angle defined between the two mounting planes of the wedge. The position after such a 180.degree. rotation is illustrated in FIG. 3. It will be noted that the rotation axis remains in its original vertical plane but has been shifted to one side only of the reference axis as shown in FIG. 3.
In the case where the rotation axis of the load 1,2,5 is shifted by an angular value B which is less than 2A with reference to the vertical reference axis of the tower 3, the new orientation of the rotation axis is sited out of the vertical plane containing the origin position and the 2A position and is shifted relative to that vertical plane by an angle equal to 2A-B, as illustrated in FIG. 5. The particular case in which the angle B is equal to the angle A produces two equal and opposite orientations with reference to the vertical plane of the tower 3 and the perpendicular vertical plane, each value equal to A.
Although the positions described are the most frequently used, it will be appreciated that any other setting of the wedge may be effected so that the two orientations for example would be situated in the same quadrant.
In all cases and for both useful positions, the articulation axes of the antenna 1 on the sighting assembly 5 are positioned in a common vertical plane.
A device of this type using a wedge with two relatively inclined mounting planes can be used with an azimuth assembly which is solidly connected with the tower 3.
A drive between the wedge 4 and the azimuth assembly 2 and the existence of a non-driven bearing on the inclined mounting plane between the wedge and the tower 3 allows for angular positioning of the load.
Although this device allows convenient adjustment of the angular orientation of the axis of the azimuth plate 2 by rotation of the wedge 4, it has the disadvantage of eliminating the relative rotation of these two elements and it is therefore necessary to use an additional rotating device to provide rotation of the antenna 1.